1. Field of the Invention
The present invention relates to an image-forming apparatus having the function of converting the tone of an image.
2. Description of the Related Art
In an image-forming apparatus having the function of exposing and printing an image recorded on a photographic film onto a photographic printing paper, for instance, it is necessary to match the latitude of the printing paper with a density range of the image recorded on the photographic film.
The contrast characteristic of an image recorded on a photographic film is determined by conditions at the time of recording, and this image is exposed onto a black-and-white printing paper, a color printing paper or the like.
Various tones ranging from a hard gradation to a soft gradation are available for black-and-white printing papers. When a black-and-white image is exposed, a printing paper having a tone suitable to the contrast of the image on the photographic film or the photographer's intent is selected.
Meanwhile, as for color printing papers, printing papers having different tones as in the case of the black-and-white printing papers are not available, and only printing papers having single tones are available. Accordingly, when a color image is exposed, the amount of exposure is only adjusted in such a manner as to match as much as possible the latitude of the density that can be expressed by the printing paper. Therefore, it is very rare that special efforts for obtaining a print of an optimum tone are made.
Furthermore, as soft gradation enhancement in accordance with the intent of the person who prepares the print, there are cases where a print is prepared in which the average density of the overall image plane is lowered, i.e., a print of a so-called high-key tone.
In a case where exposure is effected by converting the tone of an image on a photographic film to a softer tone, exposure is effected by inserting a mask having a reversed brightness pattern of an original image into the optical path of an optical system which makes up the image-forming apparatus. On the other hand, in a case where exposure is effected by changing the tone to a harder tone, exposure is effected by inserting a mask having a pattern which is identical to the brightness pattern of the original image into the optical path.
In addition, as a contrast-correcting method which does not employ a mask, a technique is known in which a liquid crystal panel having electrodes arranged in the form of a matrix is inserted into the optical path, and the transmittance of pixels is controlled to obtain a desired amount of light, as disclosed in Japanese Patent Publication No. 10819/1989. This method makes it possible to correct the contrast of an exposed image by controlling the voltage applied to the electrodes.
Image processing for suppressing the sharpness of an image is attained by scattering the image light which has passed through a photographic film and exposing the printing paper.
The scattered light of the image light is obtained by using a soft focus filter or a liquid crystal having a scattering effect. In the case where the soft focus filter is used, exposure is effected by inserting the soft focus filter into the optical path in the same way as the above-described contrast correcting method.
In a case where exposure is effected with respect to a black-and-white printing paper, although printing papers of various tones are available as described above, it does not necessary follow that printing papers of desired tones are available. On the other hand, in a case where exposure is effected on a color printing paper, substantial time and labor are required for the preparation of an appropriate mask corresponding to the image and for the inserting operation of the mask, so that skill is required.
Furthermore, in the case where exposure is effected with respect to a color printing paper by inserting the aforementioned liquid crystal panel into the optical path instead of the mask, it is necessary to control the applied voltage for each region. Hence, there is a problem in that the circuit configuration consequently becomes complex.
Accordingly, with the image-forming apparatuses of a quality which meets the standards of the market, it is difficult to effect exposure by correcting the contrast easily.
In addition, the suppression of the sharpness of the image is attained by using a soft focus filter or a liquid crystal having a scattering effect, as described above. In the case where the soft focus filter is used, substantial time and labor are required for the selection of a soft focus filter having an appropriate scattering coefficient and for the inserting operation of the soft focus filter. In the case where the liquid crystal is used, it is necessary to control the voltage applied to the liquid crystal. In the case of a liquid crystal panel arranged in the form of a matrix, it is necessary to control the applied voltage for each region.